Alloys typically have properties that vary with the contribution of the different components in the alloy. Consequently, in order to obtain materials with particular properties or in order to study the variation of properties with varying contribution of different components, screening of the properties of alloys often is performed. Whereas such screening could be performed on a large number of separately prepared samples, it is preferred to prepare a sample where a controlled variation of the composition of alloy occurs over the surface. The latter is less time and labour intensive and allows to reduce the amount of preparation materials required.
Good preparation of binary, ternary, quaternary or higher order alloys with a controlled varying composition over the surface is difficult. A technique often applied is combinatorial sputtering. Most often ternary alloys are deposited using 2, 3 or more targets. Targets thereby consist either out of a pure element or out of different elements mixed up in one target.
In one manufacturing technique for making combinatorial sputtered samples, the substrate is positioned above the targets positioned in a vacuum system, the targets all being directed towards the substrate. The flux of the different targets hit the substrate simultaneously and the variation of the distance between different positions on the substrate and the target results in different contributions of the sputtered element to the composition of the alloy deposited.
In another approach, multilayers are deposited on the substrate. The substrate is moved over the different sputter targets and for each target, a certain film thickness of the target material is deposited. In order to cover a lot of compositions in the binary, ternary or higher order phase diagram, depositions are performed using complicated masks and automated shutters, to induce the proper variation of the contribution of the different elements. Furthermore, With this approach only a discrete amount of compositions can be made and since it is an intrinsic multilayer system, deposition is slow since samples and/or shutters have to move and the samples needs to be further annealed to homogenize the sample which can cause changes in the sample.
In Chem. Mater. 2002, 14, 3519-3523, Dahn describes a multi-target sputtering machine to produce films on wafers that map large portions of ternary phase diagrams whereby the elements sputtered on the wafer vary with the position. A substrate is moved in a horizontal plane above different targets. The targets are positioned on a horizontal plate, parallel to the horizontal plane wherein the different substrates move. In between the target and the sample special designed masks are placed to have a gradient of the specific material on the sample. A “linear” mask opening and a “constant” mask opening is demonstrated. The method is demonstrated for a SiSnxAly (0<x, y<1) film on a substrate of 75×75 mm. In one direction an increasing Sn content is demonstrated and in a direction perpendicular to that direction an increasing concentration of Al is demonstrated. When the sample is positioned above a first target A a thin gradient of material A is deposited. When the sample moves from target A to target B, the sample makes a rotation over 120° around its own axis to have a gradient in a different direction. Then a gradient of material B is deposited. Moving towards a third target C, the sample again rotates around its own axis over 120°, and at target C, a thin gradient layer of material C is deposited. When the samples moves back towards target A, the sample is rotating once more in order to be in the original position when passing target A.
In Meas. Sci. Technol. 17 (2006) 1399, Dahn describes, using a similar setup, a method for the production of four-component combinatorial thin films. The system requires design of complex shadow masks and upscaling to obtain a higher resolution in composition or to use more targets is limited by the vacuum system size.